FTIR STUDY OF CHROMIUM CARBONYL-COMPLEXES ON SILICA-ALUMINA - ACTIVE ETHENE POLYMERIZATION CATALYSTS

IR spectra are reported of [Cr(CO)(3)(eta-C6H6)] and Cr(CO)(6) adsorbe d on silica-alumina. The molecules were physically adsorbed, O-ligated to two types of Lewis-acidic Al3+ site or underwent ligand loss to gi ve sub-carbonyl species which were active as ethene polymerisation cat alysts. Ligand loss was promoted by evacuation at 25 degrees C, therma l ageing at 30-80 degrees C, or exposure to ethene and involved retent ion of incompletely coordinated Cr on the surface. Contact with ethene gave highly linear polyethene chains. The efficiency of silica-alumin a as a support for active catalysts is attributed to the high populati on of strongly Lewis-acidic surface sites.